Hox genes are an ancient family of developmental regulators that help pattern the anterior-posterior axis of animal embryos. The understanding of how HOX proteins function is crucial to an understanding of how animal bodies, including the human body, develop normal morphology during embryonic development. We are fascinated by a number of questions about how Hox genes help shape embryos. One question is based on recent work showing that a microRNA gene called mir-10 is a conserved resident of Hox gene clusters in both Drosophila and mammals. We have found that Drosophila mir-10 is expressed in a pattern that resembles Hox genes and has predicted target sites in Hox messenger RNAs. We plan to isolate mutations that abolish mir-10 functions, and study the interaction between mir-10 and Hox genes in the construction of the Drosophila body plan. We also plan to develop a method to colocalize microRNAs and their target messenger RNAs in processing bodies of developing animal cells. Lessons that we learn from such studies will be applicable to how mir-10 functions in the context of developing mammalian embryos and may provide a new and rapid way of testing the physiological relevance of predicted microRNA/messenger RNA interactions. We are also interested in the functions of HOX protein domains that are conserved between Drosophila and mammals. One such domain is the N-terminal SSYF domain. Recent research indicates that this motif is the core of a HOX transactivation domain, and we will perform protein-protein interaction assays and gene interaction assays to characterize the proteins that bind and potentiate Hox transactivation function in embryos. Finally, although there are isolated cases in which HOX protein functional changes correlate with changes in animal morphology, we are interested in testing whether this is a more widespread phenomenon. So we will test whether changes in HOX protein function in two different arthropod species, Porcellio scaber and Cupiennius salei, contributed to the evolution of limb number in those two animals.